
<!DOCTYPE html>
<html>
  <head>
    <title>深蓝</title>
    <meta charset="utf-8" />
    <link rel="icon" href="jisuan.jpg" />
    <meta name="viewport" content="width=device-width" />
  </head>
  <body>
    <input id="num1" /> * <input id="num2" />
    <button onclick="jiSuan()">=</button> <input id="num3" />

    <script>
      function jiSuan(){
        num3.value = num1.value * num2.value;
      }
    </script>
  </body>
</html>